Vehicle exhaust emissions have become a major source of air pollution with the rapid development of transportation. The improvement of gasoline quality is the most important way to reduce vehicle exhaust emissions. It is known that alkylate oils obtained from alkylation reaction between isobutane and C3˜C5 olefins are sulfur-free, of high octane and small differences between research octane number and motor octane number, so that they can be used as an important blending component of high quality clean gasoline.
As a conventional technology in the field of oil refining, alkylation reaction mainly includes sulfuric acid alkylation technology and hydrofluoric acid alkylation technology, wherein isoparaffins are obtained through reaction between isobutane and olefins in the presence of a catalyst (sulfuric acid or hydrofluoric acid). The sulfuric acid alkylation method and the hydrofluoric acid alkylation method are of different technological characteristics and very close to each other in infrastructure investment, production costs, product yield, product quality, etc. Therefore, these two methods coexist in a very long period and are both widely adopted. Generally, the hydrofluoric acid alkylation apparatuses excel in apparatus number and alkylate oil yield at present. However, as environment regulations are becoming increasingly strict and due to toxic properties of hydrofluoric acid, new apparatuses tend to adopt sulfuric acid alkylation processes in recent years.
In the sulfuric acid alkylation technology, reaction is carried out in a relatively low temperature and therefore the reaction apparatuses need to possess a cooling function. In the hydrofluoric acid alkylation technology, the reaction temperatures are relatively high, so that water-cooling can generally meet the requirements. As a result, the two reactor systems are quite different from each other. Conventional sulfuric acid alkylation reactors include various types of structures, among which two are mainly used currently. They are the stepped sulfuric acid alkylation unit and the Stratco reactor (i.e., an indirect cooling reactor provided with an internal warm-taking bundle).
The reactor of the stepped sulfuric acid alkylation unit generally comprises a plurality of reaction sections, wherein the sections are separated from one another with overflow baffles and each reaction section is provided with a stirrer. The reaction products and sulfuric acid finally enter into a precipitation section to be separated and the separated sulfuric acid is introduced to a reaction section for reuse via a circulation pump, wherein the automatic evaporative cooling of the reactant isobutane is adopted. This reaction system is advantageous in that each reaction section has a high paraffin-olefin ratio and small power consumption, with no additional coolant being required. However, since the paraffins and olefins are not pre-mixed, the quality of alkylate oils is reduced and the acid consumption is increased. In addition, reactions in different sections interact with one another, so that when an abnormal operation occurs in one reaction section, the entire reactor would be affected.
One specific structure for the indirect cooling reactor provided with an internal warm-taking bundle adopts a horizontal eccentric reactor. The reactor comprises a horizontal pressure vessel as a housing, and is provided with a powerful stirrer, a circulating sleeve and a thermal-taking bundle inside the reactor. Hydrocarbon feedstocks which are fed into the reactor through one upper and one lower material inlets are mixed before a stirring impeller and then sprayed toward the impeller into the reactor. The high-speed rotating impeller is arranged at a reduced diameter portion of the reactor, so that streams inside the reactor produce a plurality of fluid flowing cavities due to impeller suction, bundle resistance, linear speed differences, etc. Therefore, sulfuric acid and hydrocarbons can be better dispersed and mixed. An emulsion of acid and hydrocarbons returns to an interior portion of the sleeve at a head portion of the reactor and flows back to the stirring impeller so as to form a high-speed circulating stream. The reactor comprises circulating materials therein. Because part of the materials react for a relatively long time, side reactions are increased and acid consumption is relatively large, which is disadvantageous for improving the octane number of the product.
U.S. Pat. No. 7,652,187 discloses a sulfuric acid alkylation process between C3˜C5 olefins and isobutane, wherein instead of the conventional mechanical stirring method, an injector is adopted to mix the reactants for reaction. However, in the sulfuric acid alkylation process, because there is a great difference between sulfuric acid and hydrocarbon materials in density, the jet mixing effect is still to be improved. U.S. Pat. No. 5,785,933 discloses a reactor system of sulfuric acid catalytic alkylation, wherein a baffle and a plurality of tangentially arranged injection pipe inlets are provided inside the reactor, so that the reactants are stirred and mixed in the reactor and mechanical moving components are unnecessary. In this technology, the static mixer principle is adopted to design a sulfuric acid alkylation reactor, but the mixing effect thereof is still to be improved.
Chinese Pat. No. 1907924A discloses an ionic liquid catalytic reaction process and a reaction apparatus, wherein hydrocarbon materials and ionic liquid catalysts react in a rotating bed reactor which is arranged in an upper portion of the reactor. A lower portion of the reactor is provided with a fluid reservoir and a central portion of the reactor is provided with a stirring apparatus. The fluid reservoir is connected to a fluid material circulating pump to define the rotating bed circulating reactor. However, the reactor is not applicable in the sulfuric acid alkylation process, because it adopts circulating material heat removal, which is not suitable for sulfuric acid alkylation releasing a great amount of heat. Furthermore, the fluid reservoir in the lower portion of the reactor and reaction material circulating operations would increase side reactions.